It’s raining cats and dogs inside the $1.4B Waterview tunnels at the moment. Water is pouring down in bucket loads as the deluge safety system is tested to make sure all the sprinklers in the tunnel ceilings and the water pressure feeding them are working correctly.
It's a critical test to make sure the deluge system does what it is designed to do – suppress fires in the tunnel, stop any fire from escalating, and to allow people to escape safely.
The tunnels are divided in 30 metre zones – there are 32 sprinklers in each zone. In total there are 173 zones in both tunnels – 5,536 sprinklers in all.
Every metre in the tunnels will get a thorough soaking as water is pumped from the five deluge tanks located in the Southern Ventilation Building – each tank contains 250,000 litres of water – into the highway of pipes feeding the sprinklers.
During the tests 100 litres of water a second drenches the tunnel pavement in each zone – an underground cloudburst so dense it is impossible to see all but a metre or two ahead.
Sprinklers only run for a minute or two during the tests, but in reality they can run for up to 60 minutes.
Equally important are the checks being made in the cross passages where the deluge valves are located.
Each zone is different. The shape of the tunnels and their height changes constantly along their 2.4 kilometre-long length and we have to be sure that everything is working as it should in the tunnels themselves and the cross passages too.
The project's soggiest phase of testing will continue until the end of next month.
The next programme of commissioning for the deluge system should be a lot drier – testing alarms and the heat sensors that trigger the sprinklers.